(1) Field of the Invention
This invention relates to a flat fluorescent lamp structure, and more particularly relates to a flat fluorescent lamp structure applied as a backlight source of a display.
(2) Description of the Related art
The cold cathode fluorescent lamp (CCFL) is a common illumination device widely applied in backlight modules of liquid crystal displays. The CCFL illuminates by using plasma, which is generated by the electrons ejected from the cathode colliding with discharge gas to ionize and excite the discharge gas atom. Then, the excited atoms in the plasma release energy by the way of radiating ultra-violet (UV) illumination to back to the ground state. The UV illumination is absorbed by the phosphor layer painted on the wall of the CCFL to generate visible light.
As the size of LCD increases, the backlight module thereof needs a bigger illumination surface with better brightness and uniformity. When the CCFL is applied in small size LCD, the CCFL provides illumination from an edge of a light guide to generate a planar light source. However, when the CCFL is applied in large size LCD, a direct type backlight module, which skips the light guide and applies a plurality of CCFLs to illuminate the LCD directly instead, is commonly used.
Flat fluorescent lamp is another light source applied in backlight module. The flat fluorescent lamp illuminates based on the theory similar to the above mentioned CCFL but with a different structure. It is noted that a planar light source, especially the one with uniform brightness, is demanded for the illumination of LCD. The direct type backlight module, which is composed of a plurality of CCFLs, has a restriction in illuminating uniformity due to the brightness difference of the gap between neighboring CCFLs and the CCFL itself. In addition, the direct type backlight module also needs higher cost and complicate assembling process. Thus, the flat fluorescent lamp is presented as a direct planar light source to meet the need of LCD.
FIG. 1A shows a top view of a typical flat fluorescent lamp, FIG. 1B shows a cross-section view of the flat fluorescent lamp along b-b cross-section. Referring to FIG. 1B, the flat fluorescent lamp structure 10 has a first substrate 12 and a second substrate 14 forming a sealed space (unlabeled) filled with discharge gas 18. Inside the flat fluorescent lamp structure 10, the opposite surfaces of the first substrate 12 and the second substrate 14 respectively are painted or coated with phosphor layer 16. Also referring to FIG. 1A, the flat fluorescent lamp 1 has electrodes 11 formed on the opposite edges of the flat fluorescent lamp structure 10 to generate current. As the current is generated, the flat fluorescent lamp illuminates by the way the above mentioned CCFL does.
Also referring to FIG. 1C, which is a cross-section view along c-c cross-section of FIG. 1A, a plurality of wall structure 13 is assembled between the first substrate 12 and the second substrate 14 to form a plurality of illuminating chambers 15. The illuminating chambers 15 are structurally similar to a plurality of CCFLs arranged side by side.
It is noted that the process of fabricating the flat fluorescent lamp structure 10 usually has the first substrate 12, the wall structure 13, and the second substrate 14 assembled as a whole before vacuuming the illuminating chambers 15 and injecting discharge gas 18. In order to facilitate the vacuuming and the injecting processes, some tunnels 17 are formed through the wall structure 13 between illuminating chambers 15 to have all the illuminating chambers 15 communicating with each other.
However, the existing of tunnels 17 may hinder the lighting of illuminating chambers 15. Also referring to FIG. 1D, which shows an equivalent circuit diagram of the flat fluorescent lamp of FIG. 1A. The discharge gas 18 within the illuminating chambers 15 of FIG. 1A may be regarded as resistors R1, R3, R5, R7, and R9 of FIG. 1D respectively when discharging. For the same reason, the discharge gas 18 within the tunnels 17 of FIG. 1A may be regarded as resistors R2, R4, R6, and R8 of FIG. 1D respectively. The demanded current is provided by a current providing circuit, for example, power supply circuit 22.
It is understood that resistance is proportional to the ratio of length and cross-section area. The content mentioned below is based on the theory.
Ordinarily, the wall structure 13 of FIG. 1C is formed on the first substrate 12 by using thermal forming or sand blasting technology. The tunnels 17 with a cross-section area substantially close to the cross-section area of the illuminating chambers 15 are usually preserved at the same time. Since the length of the tunnel 17 is smaller than the length of the illuminating chamber 15. The resistance of the resistors R2, R4, R6, and R8 with respect to the tunnels 17 is much smaller than the resistance of the resistors R1, R3, R5, R7, and R9 with respect to the illuminating chambers 15.
On the other hand, the fabrication process in reality may result in variation of individual illuminating chambers 15. That is, the resistance of the resistors R1, R3, R5, R7, and R9 may not be the same. Thus, the non-uniformity of current distributed within the flat fluorescent lamp 1 seems unpreventable. When the non-uniformity of current becomes serious, even some illuminating chambers cannot be lighted to result in non-uniformity of lighting. Take the resistor R1, R2, and R3 of FIG. 1D for example. As the resistance of resistor R3 is small than the resistor R1 in reality, and the resistance of serially connected resistors R3 and R2 is smaller than that of the resistor R1 (R3+R2>R1), part of the current predicted to flow through the illuminating chamber 15 with respect to the resistor R1 flows through the tunnel 17 with respect to the resistor R2 and the illuminating chamber 15 with respect to the resistor R3. Thus, the illuminating chamber 15 with respect to resistor R1 may not be lighted so as to result in a failure flat fluorescent lamp attending with the increasing of cost.
Accordingly, in regard of the existing drawback as mentioned above, how to promote the drawback by effectively improving the non-uniformity of lighting of the flat fluorescent lamp has become an object in the present LCD industry.